A team of climate scientists in the UK has launched an ambitious citizen science effort to quickly assess the role that manmade global warming may have played in that region's extraordinarily wet winter.

The program, known as the Weather@Home 2014 project, is part of a longer term and international push to develop scientific techniques to gain insight into the relationship between global warming and extreme weather events, from heavy precipitation events to heat waves.

The winter of 2013-14 was one of the UK's wettest on record, with many areas experiencing prolonged and damaging flooding, the total cost of which is likely to reach into the billions of dollars. The flooding resulted from a seemingly never-ending parade of North Atlantic storms that struck the area, bringing heavy rains, snow and high winds.

In Oxford, for example, the period of December to February was the wettest in more than 250 years, eclipsing all previous benchmarks since they started keeping track in 1767.

While the UK Met Office has already said that the excessively wet winter is consistent with global warming's effects on the climate system, the new project is the first specific study aimed at quantitatively attributing the heavy precipitation and flooding, including assessing the role that global warming may have played.

To successfully complete such a climate change attribution study, though, the researchers need to run thousands of computer model analyses, some that include manmade global warming (specifically the increase in atmospheric concentrations of heat-trapping gases such as carbon dioxide), and some without. To dodge the need for immediate access to scarce supercomputing capacity, the Weather@Home project, which is part of the larger climateprediction.net program, is turning to the public for help.

They are asking people to download a computer program that runs climate model simulations and reports the results back to the research team, effectively creating a distributed network of supercomputers. The project is the climate science equivalent of the SETI@Home Project, which has enlisted the public's support to search for extraterrestrial life.

So, to do this, we are asking for the help of the general public. We need to run two very large “ensembles” of weather simulations, one representing conditions and “possible weather” in the winter we have just had, and one representing the weather in a “world that might have been” if we had not changed the composition of the atmosphere through greenhouse gas emissions. By comparing the numbers of extreme rainfall events in the two ensembles, we can work out if the risk of a wet winter has increased, decreased or been unaffected by human influence on climate. The ensembles need to be as big as possible to obtain robust estimates of the probability of rare events. We expect to obtain results within a month from launch, and plan to publish results as they come in, so participants will be able to see the result as it emerges.

In an unusual move, the climate scientists are publishing the results online as they come in, thereby potentially increasing the public's sense of buy-in with this effort.

Previous work by the same group found that 20th-century manmade greenhouse gas emissions increased the risk of floods occurring in England and Wales in the fall of 2000 by more than 20%. That study also relied on a distributed computing approach.

A NASA MODIS satellite image showing a series of three storms lined up across the North Atlantic.

The heavy rains in 2000 caused flooding that resulted in $2 billion in damage. Other studies have also shown that global warming has increased the odds of particular extreme heat events, such as the deadly European heat wave in 2003.

In general, the global atmosphere is carrying about 4% more water vapor than it used to, thanks to increasing air and ocean temperatures. This gives storms an added dose of energy, and allows them to drop more precipitation in intense bursts than they used to. Based on such trends, a recent study found that damage costs from European floods are expected to climb five-fold by 2050.

Linking specific extreme precipitation events to global warming is extremely complex, and requires running thousands of computer model simulations to compare the world as human activities have modified it with a hypothetical world without added greenhouse gases. On their website, the scientists wrote:

"It will never be possible to say that any specific flood was caused by human-induced climate change alone, in the sense that, without climate change, that flood would not have happened. Occasional floods have been a feature of British weather since time immemorial. We can, however, ask and answer the question how the odds of getting an extremely wet winter has changed due to man-made climate change: have past greenhouse gas emissions and other forms of pollution “loaded the weather dice” towards (or perhaps even away from) and event of this nature?"

So far, the emerging results show higher odds of a record wet winter now that global warming is taking place, compared to a world without added greenhouse gases in the atmosphere. But it's not yet clear whether the increase in odds is statistically significant.

On a broader scale, climate scientists are hoping to make major strides in climate attribution studies during the next decade, perhaps getting to the point where they can issue reliable estimates about global warming's role in an extreme event before the event is even finished. Today, most such analyses come out at least six months after an extreme event, limiting their usefulness to policymakers and the public.

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